[Is it possible to extract intracranial pressure information based on the EEG activity?] / Es posible obtener informacion de la presion intracraneal a partir de la actividad electroencefalografica?

INTRODUCTION: The capability of the electroencephalography (EEG) of recording the bioelectrical activity of the brain has made of it a fundamental tool for the evaluation of the patient's neurological condition. In recent years, moreover, it has also begun to be used in obtaining information for other kind of variables, as the ones related with the cerebral hemodynamics. AIM: To study the potential relationship between the EEG activity and the intracranial pressure (ICP) in patients suffering from traumatic brain injury and subarachnoid hemorrhage, during their stay at the intensive care unit. PATIENTS AND METHODS: Twenty-one adult patients (10 women) were included in the present observational prospective cohort study. They suffered from either traumatic brain injury or subarachnoid hemorrhage, requiring continuous EEG and ICP monitoring. In every patient, Granger causality between spectral functions of the EEG and the ICP was evaluated. Temporal windows of 10 minute were used to evaluate whether a causal relationship between those variables exist or not. In all of the cases, several days of continuous recording and assessment were performed. RESULTS: In most patients and during most of the time, Granger causality turns out to be significant in the direction from the EEG to the ICP, meaning that the EEG dynamics actually leads the ICP dynamics. CONCLUSIONS: The present work provides useful information and shed light in discovering a hidden relationship between the ICP and EEG dynamics. The potential use of this relationship could lead to develop a medical device to measure ICP in a non-invasive fashion.

TITLE: Es posible obtener informacion de la presion intracraneal a partir de la actividad electroencefalografica?Introduccion. El electroencefalograma (EEG) permite obtener informacion directa de la actividad bioelectrica del cerebro y es una herramienta fundamental para la evaluacion de la condicion neurologica del paciente. En los ultimos años ha comenzado a emplearse tambien para obtener indirectamente informacion sobre la hemodinamica cerebral y las variables que intervienen en la autorregulacion del flujo sanguineo cerebral. Objetivo. Estudiar la posible relacion entre la actividad electroencefalografica y la presion intracraneal (PIC) en pacientes con traumatismo craneoencefalico y hemorragia subaracnoidea ingresados en cuidados intensivos. Pacientes y metodos. Se incluyo a 21 pacientes (10 mujeres) mayores de 18 años con traumatismo craneoencefalico o hemorragia subaracnoidea que requerian monitorizacion de la PIC y a los que se les registro el EEG de forma continua. Se determino la causalidad de Granger entre la PIC con respecto a las variables espectrales del EEG para ventanas temporales de 10 minutos durante la estancia en cuidados intensivos. Resultados. La causalidad de Granger mostro una alta correlacion entre la PIC con las bandas del EEG. En la mayoria de los pacientes existe una causalidad de Granger significativa en la direccion del EEG hacia la PIC en gran parte del tiempo de monitorizacion, de forma que las variables del EEG precedian a la PIC. Conclusiones. El presente trabajo expone la relacion temporal subyacente entre la dinamica de la PIC y la actividad bioelectrica cerebral registrada mediante EEG en pacientes con traumatismo craneoencefalico y hemorragia subaracnoidea. El potencial uso de esta relacion podria permitir estimar la PIC de manera no invasiva.

[When does post-ictal period start in temporal lobe epilepsy? A quantitative EEG perspective]. / Donde comienza el periodo postictal en la epilepsia del lobulo temporal? Hacia una definicion cuantitativa.

INTRODUCTION: In partial seizures, from a clinical point of view or even from electroencephalography characterization of post-ictal period can be difficult. The spectral and complex network analysis could lead to a more accurate definition of its limits, as well as to a great understanding of the seizures. PATIENTS AND METHODS: Digital EEG recordings from scalp and foramen oval electrodes were used, 32 seizures, from 15 patients with drug-resistant mesial temporal lobe epilepsy (Engel I). We analyzed numerically: the spectral entropy, the different frequency bands and several variables used to characterize the cortical network, density of links, modularity, cluster coefficient and average path length. Variations of for post-ictal versus pre-ictal periods were quantified. RESULTS: The cortical network density of links increased during the post-ictal period of complex seizures matching with an spectral entropy decrease, mainly due to an increase in Delta band activity. This variables reached extreme values around one minute after seizure end, defined by classical electroencephalography. CONCLUSIONS: Our results can be explained by the appearance of an 'ending' mechanism that starts in the ictal period, classically defined, and reach their maximum effect during the post-ictal period. These results could be useful to define the post-ictal period start, as the moment with maximum synchrony, which has a highest density of links and a lowest spectral entropy.

TITLE: Donde comienza el periodo postictal en la epilepsia del lobulo temporal? Hacia una definicion cuantitativa.Introduccion. En las crisis parciales, el periodo postictal presenta grandes dificultades de caracterizacion, tanto desde el punto de vista clinico como en electroencefalografia. Un analisis espectral y de redes complejas permitiria una definicion mas precisa de sus limites y una comprension mas completa de las crisis. Pacientes y metodos. Se analizaron registros digitales de electroencefalografia de electrodos de scalp y foramen oval, 32 crisis, de 15 pacientes con epilepsia farmacorresistente del lobulo temporal (Engel I). Numericamente se estudio la entropia espectral, las distintas bandas de frecuencia y medidas de caracterizacion de la red cortical, la densidad de enlaces, la modularidad, el coeficiente de agrupamiento y la longitud de camino medio, y se cuantifico la variacion del periodo postictal respecto al preictal. Resultados. Durante el periodo postictal de las crisis complejas existe un marcado aumento de la densidad de enlaces en la red cortical coincidente con un descenso en la entropia espectral, principalmente debido al aumento de la actividad en la banda delta. Los valores extremos de estas medidas se alcanzan aproximadamente un minuto despues del fin de las crisis, definidas electroencefalograficamente usando metodos tradicionales. Conclusiones. Nuestros resultados pueden explicarse por la aparicion de un mecanismo de 'finalizacion' de las crisis que comienza dentro del periodo ictal definido clasicamente y que alcanzan su efecto maximo durante el periodo postictal. Estos resultados podrian emplearse para definir el inicio del periodo postictal como aquel donde la sincronizacion es maxima, esto es, donde la densidad de enlaces resulta mayor y la entropia espectral es minima.

Electrocorticographic evidence and surgical implications of different physiopathologic subtypes of temporal epilepsy.

OBJECTIVE: Mesial temporal lobe epilepsy (MTLE) might have a focal or a network physiopathology. Therefore, the objective of this study was to demonstrate that changes in the spiking activity during electrocorticography (ECoG) could reflect changes in the epileptic network, and the resection of the epileptogenic zone could eliminate the mesial spikes. METHODS: Twenty-five MTLE patients were intraoperatively evaluated by ECoG and the mesial strip was maintained until the lateral cortectomy (LC) was completed. Total spiking activity (TSA, mean spikes/min for all the mesial channels) was computed off-line before and after LC. Either a tailored anterior medial temporal resection or LC was carried out based on the TSA changes. RESULTS: The outcome at 19.1±1.4 months was Engel's class I, 84%; II, 8%; or III, 8%. During the LC, the TSA recorded from the mesial strip did not change in 14 patients, increased in three patients, and decreased in eight patients. In 20% of patients, the mesial activity completely disappeared, and the mesial structures were spared. All of these patients were Engel's class IA. CONCLUSIONS: Our results strongly suggest the existence of physiopathologic differences in MTLE. The identification of these subtypes is fundamental for an individualized surgical approach. SIGNIFICANCE: ECoG would be needed to offer a better surgical approach.

[Contamination of paroxysmal activity in quantitative EEG methods in epileptic patients]. / Contaminacion de la actividad paroxistica en los metodos cuantitativos de electroencefalografia en pacientes epilepticos.

INTRODUCTION. The presence of an acute spike-wave pattern in the recordings of epileptic patients can contaminate the calculated synchronisation values between pairs of electrodes. MATERIALS AND METHODS. We present a simple procedure, involving a numeric simulation of a bivariate electroencephalogram recording with paroxysmal activity, to determine whether or not a method for quantifying synchronisation must be used on any of the recordings that are typically employed in the preoperative evaluation of patients with epilepsy. RESULTS. The information provided by this procedure makes it possible to distinguish between the authentic synchronisation of baseline activity and that produced by paroxysmal activity, such as acute spike-wave patterns. The procedure developed in this study makes it possible to quantify the degree of 'contamination' produced by the synchronisation of the paroxysmal activity on the synchronisation values of the baseline activity. CONCLUSIONS. The issue addressed in this work is of fundamental importance when automatic methods are utilised in the clinical applications of quantitative electroencephalography and can help to prevent diagnostic errors in which synchronisation is used as a marker of the pathology.

[Voltage sources in mesial temporal area induced by etomidate]. / Fuentes de voltaje en la region temporal mesial inducidas por etomidato.

INTRODUCTION: It has been recently shown that activation of the EEG by etomidate is a specific and safe technique during the evaluation of patients for epilepsy surgery. AIM: To analyze the pathophysiological properties of interictal activity induced by etomidate and compare with the interictal spontaneous activity. PATIENTS AND METHODS: We studied 13 patients by video-EEG with foramen ovale electrodes. Etomidate (0.1 mg/kg) was injected to activate the epileptogenic region. The activity of foramen ovale electrodes was adjusted to a monopolar voltage source. RESULTS: Interictal activity mediated by etomidate fits well to a monopolar model, in the same way that the basal interictal activity. The voltage sources distribution recorded during the interictal activity and distribution of voltage sources recorded in presence of etomidate have similar topographical properties. The equivalent charge induced by etomidate was higher than the basal one. CONCLUSIONS: The basal and etomidate induced activity have similar electrophysiological properties, suggesting that the same or similar structures are responsible of both. So, etomidate can be used as an specific inductor of EEG activity during presurgical evaluation.

Role of transport performance for neuron cell morphology.

The compartmental model is a basic tool for studying signal propagation in neurons; if the model parameters are adequately redefined, it can also be helpful in the study of electrical or fluid transport in other biological systems. Here we show that the input resistance in different networks that simulate the morphology of neurons is the result of the interplay between the relevant conductances, neuron morphology, and neuron size. The results suggest that neurons may grow in such a way that facilitates the current flow to the synapses, concurrently minimizing power consumption.

[The pathophysiological foundations of temporal-lobe epilepsy: studies in humans and animals]. / Bases fisiopatológicas de la epilepsia del lóbulo temporal: estudios en humanos y animales.

INTRODUCTION: Temporal lobe epilepsy (TLE) is the most frequent form of pharmaco-resistant epilepsy in human. Research using material from TLE patients undergoing surgery and animal models has significantly increased in the last decade. DEVELOPMENT: We review recent findings obtained over the last years from electrophysiological and anatomical studies in human and animal models of TLE. Data suggest a large heterogeneity and inter-individual variability depending on the model and the system under study. However, a common principle that appears to underlie the epileptic condition is the reorganization of excitation and inhibition resulting in hyperexcitability. Recent research combining in vitro electrophysiology together with depth recordings in vivo and new analytical methodologies is also discussed. CONCLUSIONS: A multidisciplinary approach using both human and animal models can help to fill gaps in our knowledge and to provide unique insights into the pathophysiology of TLE.

Detecting determinism in high-dimensional chaotic systems.

A method based upon the statistical evaluation of the differentiability of the measure along the trajectory is used to identify determinism in high-dimensional systems. The results show that the method is suitable for discriminating stochastic from deterministic systems even if the dimension of the latter is as high as 13. The method is shown to succeed in identifying determinism in electroencephalogram signals simulated by means of a high-dimensional system.

Statistical and dynamical analysis of circadian rhythms.

Time series of core temperature in golden hamsters with or without access to a running wheel were analyzed using statistical tools and Dynamical Systems theory. Although the statistical analysis did not show any striking difference between the two groups (other than clearer spectra in the case in the animals with access to wheels), a clear dynamical difference was found. The circadian temperature of hamsters with access to wheel running exhibited fewer degrees of freedom than those without access to them (1.728 vs 11.548). Thus, it may be argued that wheel running synchronizes the ciradian organization of hamsters.